With the continuous development of communication technologies, a relay (Relay) technology is proposed as a key technology used to increase the cell capacity and extend the coverage. Problems that existing cellular systems are faced with can be solved effectively by deploying a relay node (Relay Node; RN for short) on a network to enhance radio communication signals between a base station and a terminal. In addition, because the RN has such characteristics as low software costs, low hardware costs, low deployment costs, and flexible deployment, it has attracted wide attention and is researched by more and more operators and vendors.
In brief, the RN is a node that transfers data between the base station and the terminal, so that a radio signal can reach a destination through multiple transmissions (multiple hops). After the RN accesses a conventional base station, the conventional base station may be referred to as a donor base station (Donor evolved NodeB; DeNB for short). In the Third Generation Partnership Project (Third Generation Partnership Project; 3GPP for short) standard, the radio interface between the RN and the donor base station is a Un interface, and the radio interface between the user equipment (UE) and the RN is a Uu interface.
In an RN implementation solution in the prior art, the RN accesses a network in a mode similar to the access mode used by the UE. The RN establishes a signaling bearer and a user data bearer with the network. All signaling and data related to a UE that camps on the RN are transmitted through the user data bearer between the RN and the network. However, the user data bearer can provide only cipher protection. Therefore, only the cipher protection is available when control plane signaling related to the UE that camps on the RN is transmitted between the RN and the donor base station.
The control plane signaling related to the UE that camps on the RN includes access stratum (Access Stratum; AS for short) signaling and non access stratum (Non Access Stratum; NAS for short) signaling that are exchanged between the UE and the network, and signaling that is exchanged inside the network for the purpose of providing the UE with services, such as S1 interface signaling defined in a long term evolution (Long Term Evolution; LTE for short) system. The S1 interface signaling includes signaling of sensitive information, for example, signaling for transmitting a key Kenb used to protect the Uu interface communication. Because the above signaling can only be transmitted over the user data bearer on the RN, only the cipher protection is available to the signaling according to the RN implementation solution in the prior art. Even if the cipher protection is available, attackers can manipulate the key Kenb obtained by the RN by altering the signaling, which may cause attacks, such as a denial of a service attack.